This study is based on a typical residual soil landslide adjacent to Daxishan Reservior in Dalian city of China. By drilling the original samples in the field and remodeling the copy samples in the laboratory, a series of geotechnical experiments are carried out by the improved direct shear apparatus to obtain the changing law between the shear strength and water content of the mixed slide-zone soils. Emphasis is given on the shear stress-strain behavior and the corresponding constitutive model under different water content for the soils. Especially, the typical fitting equation is achieved to reflect the state of shear stress-normal stress-water content, some strain softening and hardening behavior on the mixed slide-zone soils of landslide is also discussed in detail. The results indicate that the shear strength is significantly related to water content of mixed slide-zone soils of landslide. The bigger water content of slide-zone soil is, the smaller the shear strength of soils is. When water content of mixed slide-zone soils approaches to certain value (i.e., 15%), the curve of shear stress and displacement shows a remarkable softening behavior, and the shear strength has marked a peak value.